Using plated surface for recording media without polishing

ABSTRACT

Ultra smooth as-deposited composite nickel coatings for use in an information storage system are provided. The composite nickel coatings include an electrolessly deposited nickel layer formed on a sputter deposited nickel layer. The composite nickel coatings have an as-deposited surface roughness of less than about 10 Å. Embodiments include formation of the composite nickel coating on a disk, followed by deposition of an underlayer and magnetic layer thereon to form a magnetic recording medium.

CROSS REFERENCE TO A RELATED APPLICATION

This application claims priority benefit of U.S. Provisional PatentApplication Ser. No. 60/232,897 filed Sep. 15, 2000, entitled USINGPLATED SURFACE FOR RECORDING MEDIA WITHOUT POLISHING in the name ofConnie C. Liu, Linda L. Zhong, Ian J. Beresford, Lin Huang, Joseph Leighand David E. Brown, which is herein incorporated by reference in itsentirety.

This is a divisional of application Ser. No. 09/895,053 filed on Jun.29, 2001 now U.S. Pat. No. 6,689,413.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present invention relates to nickel-coated substrates. The inventionhas particular applicability to the manufacture of magnetic recordingmedia.

2. Description of the Background Art

Nickel (Ni) plating, particularly electroless Ni platings or deposits,enjoys technological applicability in various industries, such as theelectronic, oil and gas, aerospace, machinery, automobile and magneticrecording media industries. For example, in magnetic recording mediaapplications, a magnetic disc comprising a non-magnetic substrate suchas aluminum (Al) or an aluminum alloy may be coated with an amorphousnickel deposit.

Magnetic disk drives are normally operated using a contact start-stop(CSS) method. In the CSS method, a head begins to slide against thesurface of the magnetic disk as the disk begins to rotate and, uponreaching a predetermined rotational speed, the head floats in air afixed distance above the surface of the disk. The distance that the headfloats above the surface of the disk is called the flying height. Thehead floats above the surface of the disk due to dynamic pressureeffects caused by the air flow generated between the recordingoperations of a disk drive, the head is maintained at a controlleddistance from the surface of the magnetic disk, supported on a bearingof air as the disk rotates. Upon terminating operation of the diskdrive, the rotational speed of the magnetic disk is decreased such thatthe head begins to slide against the surface of the disk, until iteventually stops, in contact with and pressing against the disk. Thus,each time the head and disk assembly is driven, the sliding surface ofthe head repeats this cyclic operation consisting of stopping, slidingagainst the surface of the disk, floating in air, sliding against thesurface of the disk and stopping.

In order to achieve high areal density for magnetic disk drives, it isconsidered necessary to minimize the flying height of the head above thesurface of the magnetic disk. One technique for minimizing the flyingheight of the head above the surface of the magnetic disk usessubstrates having an extremely smooth, defect-free surface forfabricating such magnetic disks. The absence of defects such as, forexample, pits is especially important, since pits may adversely affectthe writing of information to the magnetic disks.

For manufacturing magnetic recording media, amorphous nickel plating isconventionally applied to a non-magnetic substrate, such as, forexample, aluminum (Al) or an Al-alloy substrate. Electroless plated NiPis typically chosen because it exhibits desirable physical and chemicalproperties, such as hardness, lubricity, appearance, and corrosionresistance.

It is recognized, however, that electroless metal plating, such aselectroless NiP plating known to the art, does not achieve coatingsexhibiting a desired degree of surface smoothness, particularly thedegree of smoothness necessary to satisfy the high areal recordingdensity objectives of current magnetic recording media (e. g., anaverage surface roughness (Ra) less than about 30 Å). Marketcompetitiveness further requires achievement of ultra-smooth electrolessnickel coatings on non-magnetic substrates with increased manufacturingthroughput and higher yield.

Conventional techniques for improving the surface smoothness of platednickel coatings include the incorporation of a polishing step subsequentto the electroless metal plating. Polishing, however, requires aconsiderable capital investment and results in reduced processthroughput.

Accordingly, there exists a need for as-deposited ultra-smooth nickelcoatings having reduced defects that do not require subsequentpolishing. There exists a particular need for methodology enabling thedeposition of amorphous nickel coatings on non-magnetic substrates,which have an as-deposited surface roughness (Ra) less than about 30 Å.

SUMMARY OF THE INVENTION

An information storage system employing a magnetic recording media isprovided. The magnetic recording media comprises a non-magneticsubstrate having a composite nickel coating thereon is provided. Thecomposite nickel coating includes an electrolessly deposited nickellayer formed on a sputter deposited nickel layer. The as-depositedcomposite nickel coating has a surface roughness (Ra) less than about 10Å.

A method of manufacturing a magnetic recording media for use in aninformation storage system is also provided. The method includes forminga composite nickel coating on a non-magnetic substrate wherein thecomposite nickel coating comprises an electrolessly deposited nickellayer formed on a sputter deposited nickel layer. The as-depositedcomposite nickel coating has a surface roughness (Ra) less than about 10Å.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the present invention will becomeapparent upon reading of the detailed description of the invention andthe appended claims provided below, and upon reference to the drawingsin which:

FIG. 1 depicts a graph of the surface roughness for a composite nickelcoating of the present invention plotted as a function of the thicknessof an underlying sputtered NiP layer;

FIG. 2 schematically illustrates a magnetic recording medium to whichthe present invention is applicable; and

FIG. 3 shows a magnetic recording medium in an information storagesystem in accordance with the present invention.

DETAILED DESCRIPTION

The present invention advantageously achieves formation of compositenickel coatings on non-magnetic substrates having a surface roughness(Ra) less than about 10 Å. The achievement of such ultra-smoothas-deposited composite nickel coatings yields several technologicaladvantages. For example, after the composite nickel coating is formed onthe non-magnetic substrate, the high degree of surface smoothnesseliminates the need for a subsequent polishing step. As such, thecomposite coated substrate may be used directly for a media depositionprocess, improving the overall process throughput for the manufacture ofmagnetic recording media. The composite nickel coatings having anas-deposited ultra-smooth surface enables and facilitates themanufacture of magnetic recording medium having high areal recordingdensity, with reduced flying heights for the head.

The present invention stems from the discovery that the deposition of asputtered nickel layer on a substrate prior to the deposition of anelectrolessly plated nickel layer thereover provides a composite nickelcoating having a surface roughness that is significantly smoother thanthat of traditionally deposited electroless nickel layers. Furthermore,as illustrated in FIG. 1, the degree of surface smoothness appears to beenhanced as the thickness of the underlying sputtered nickel layer isincreased.

The composite nickel coatings of the present invention are applicable tothe manufacture of magnetic recording medium, as depicted in FIG. 2. Themagnetic recording medium comprises a substrate 10, typically formed ofglass or glass-ceramic materials. Alternative substrates may includemetal matrix composites, reacted metal-ceramics, aluminum alloys suchas, for example, aluminum-magnesium (AlMg), as well as graphite andmetal matrix composites, such as B₄C—Al.

The substrate 10 may be ground, lapped or polished in order to reducethe surface roughness thereof before the composite nickel coating isapplied thereto. Also, the substrate should preferably have amacro-waviness (undulations across the surface thereof) that is lessthan about 1000 Å.

The magnetic recording medium is typically deposited on both sides ofthe substrate 10. Typically, an adhesion enhancement layer 11, 11′ isdeposited on the substrate 10 to improve the adhesion of subsequentlydeposited layers thereon. Suitable materials for the adhesionenhancement layer include chromium and chromium alloys, as well astitanium tungsten (TiW).

The composite nickel coating 20 comprising a sputter deposited nickellayer 12 a, 12 a′ and an electrolessly deposited nickel layer 12 b, 12b′ is formed on the substrate 10. The sputter deposited nickel layer 12a, 12 a′ is formed on adhesion enhancement layer 11, 11′. The sputterdeposited nickel layer 12 a, 12 a′ may comprise NiP formed from a NiPtarget comprising about 15 atomic % to about 30 atomic % nickel (Ni).The sputter deposited nickel layer 12 a, 12 a′ preferably has athickness within a range of about 10 Å to about 1000 Å.

After the sputter deposited nickel layer 12 a, 12 a′ is deposited, theelectrolessly deposited nickel layer 12 b, 12 b′ is formed thereon. Theelectroless nickel plating bath employed in the present invention may bea conventional electroless composition such as is disclosed in U.S. Pat.No. 4,567,066, and those disclosed in Hajdu, J. B. et al., “THEELECTROLESS NICKEL PROCESS FOR MEMORY DISKS,” The ElectrochemicalSociety Magnetic Materials, Processes, and Devices, Electro-DepositionProceedings, Vol. 92–10, pp. 39–55 (1992), and which are incorporated byreference.

Electroless nickel plating compositions generally comprise fouringredients dissolved in a solvent, typically water. These ingredientsinclude: (1) a source of Ni ions; (2) a reducing agent, such as ahypophosphite or an amine borane; (3) an acid or hydroxide pH adjusterto provide a suitable pH; and (4) a complexing agent for metal ionssufficient to prevent their precipitation in solution. When ahypophosphite is used for the reducing agent, the deposit will containNi and P. On the other hand, if an amine borane is used for the reducingagent, the deposit will contain Ni and boron (B).

Ni ions can be provided by employing a suitable soluble salt, such asnickel sulfate, nickel chloride, nickel acetate and mixtures thereof.The concentration of Ni in solution can vary widely. Ni concentrationsare typically within a range of about 0.1 g/l to about 100 g/l.

The reducing agent employed, particularly in manufacturing a magneticrecording medium, is typically a hypophosphite ion supplied to the bathby any suitable source, such as sodium hypophosphite, potassiumhypophosphite, ammonium hypophosphite, and nickel hypophosphite. Otherreducing agents, such as amine boranes, borohydrides and hydrazine, canalso suitably be employed. The concentration of the reducing agent isgenerally in excess of the amount sufficient to reduce the Ni in thebath.

The plating bath can be acid, neutral or alkaline, and the acid oralkaline pH adjuster can be selected from a wide range of materials,such as ammonium hydroxide, sodium hydroxide, and hydrochloric acid. ThepH of the bath may range from about 2 to about 12.

The complexing agent can be selected from a wide variety of materials,such as lactic acid, malic acid, and those containing anions such asacetate, citrate, glycolate, pyrophosphate, and mixtures thereof. Rangesfor the complexing agent, based on the anion, can vary widely with arange of about 1 g/l to about 300 g/l.

The electroless Ni plating baths employed in the present invention canalso contain other conventional additives, such as buffering agents,bath stabilizers, rate promoters, brighteners, etc. Stabilizers such aslead, antimony, mercury, tin and oxy compounds, such as iodate, can alsobe employed. Suitable electroless plating baths can be formed bydissolving the ingredients in water and adjusting the pH within thedesired range.

The incorporation of certain metal ions in a plating bath forelectroless Ni deposition additionally enhances the smoothness of theas-deposited surface, as disclosed in U.S. Pat. No. 6,106,927. Suitablemetal ions may include Al and/or Cu ions. The metal ions can beincorporated in the electroless Ni plating bath in any of various forms,such as a salt. For example, Al ions may be provided to the plating bathfrom aluminum sulfate, e.g., Al₂(SO₄)₃ 16H₂O, and Cu ions from coppersulfate (CuSO₄). The concentration of Al ions in the plating bath ispreferably less than about 20 parts per million (ppm), while theconcentration of Cu ions in the plating bath is preferably within arange of about 5 ppm to about 10 ppm.

In accordance with embodiments of the present invention, theelectrolessly deposited nickel coatings 12 b, 12 b′ may have a thicknesswithin the range of about 0.5 microns to about 10 microns, deposited ata temperature within a range of about 25° C. to about 100° C.

The degree of surface smoothness achieved for the composite nickelcoating of the present invention may be appreciated with reference tothe following examples.

EXAMPLE 1

A nickel phosphorus (NiP) composite coating was prepared. The NiPcomposite coating was prepared by sputtering a nickel-phosphorus (NiP)layer on a TiW coated Ohara TS-10 SXSP glass-ceramic disk. The NiP wassputtered from a NiP target comprising about 25 atomic % nickel. Thesputter deposited NiP layer had a thickness of about 1000 Å. A 1 micronthick nickel phosphorus (NiP) layer was electrolessly deposited over thesputter deposited NiP layer. The NiP layer was electrolessly plated froman Enthone 6450 Ni plating bath.

The surface roughness of the as-deposited composite nickel layer wasmeasured using AFM (Atomic Field Microscopy). A 10 micron×10 micron scanof the composite nickel coating indicated a surface roughness (Ra) ofabout 3.2 Å.

EXAMPLE 2

A nickel phosphorus (NiP) composite coating was prepared. The NiPcomposite coating was prepared by sputtering a nickel-phosphorus (NiP)layer on a TiW coated Ohara TS-10 SXSP glass-ceramic disk. The NiP wassputtered from a NiP target comprising about 25 atomic % nickel. Thesputter deposited NiP layer had a thickness of about 500 Å. A 1 micronthick nickel phosphorus (NiP) layer was electrolessly deposited over thesputter deposited NiP layer. The NiP layer was electrolessly plated froman Enthone 6450 Ni plating bath.

The surface roughness of the as-deposited composite nickel layer wasmeasured using AFM (Atomic Field Microscopy). A 10 micron×10 micron scanof the composite nickel coating indicated a surface roughness (Ra) ofabout 5.6 Å.

EXAMPLE 3

A nickel phosphorus (NiP) composite coating was prepared. The NiPcomposite coating was prepared by sputtering a nickel-phosphorus (NiP)layer on a TiW coated Ohara TS-10 SXSP glass-ceramic disk. The NiP wassputtered from a NiP target comprising about 25 atomic % nickel. Thesputter deposited NiP layer had a thickness of about 200 Å. A 1 micronthick nickel phosphorus (NiP) layer was electrolessly deposited over thesputter deposited NiP layer. The NiP layer was electrolessly plated froman Enthone 6450 Ni plating bath.

The surface roughness of the as-deposited composite nickel layer wasmeasured using AFM (Atomic Field Microscopy). A 10 micron×10 micron scanof the composite nickel coating indicated a surface roughness (Ra) ofabout 5.5 Å.

EXAMPLE 4

A nickel phosphorus (NiP) composite coating was prepared. The NiPcomposite coating was prepared by sputtering a nickel-phosphorus (NiP)layer on a TiW coated Ohara TS-10 SXSP glass-ceramic disk. The NiP wassputtered from a NiP target comprising about 25 atomic % nickel. Thesputter deposited NiP layer had a thickness of about 100 Å. A 1 micronthick nickel phosphorus (NiP) layer was electrolessly deposited over thesputter deposited NiP layer. The NiP layer was electrolessly plated froman Enthone 6450 Ni plating bath.

The surface roughness of the as-deposited composite nickel layer wasmeasured using AFM (Atomic Field Microscopy). A 10 micron×10 micron scanof the composite nickel coating indicated a surface roughness (Ra) ofabout 5.5 Å.

Referring again to FIG. 2, after the composite nickel coating 20 isformed on the substrate 10 the magnetic medium is deposited thereon. Themagnetic medium typically includes an underlayer 13, 13′, such aschromium or a chromium alloy, a magnetic layer 14, 14′, such as acobalt-based alloy, and a protective overcoat 15, 15′ such as acarbon-containing material. Typically, although not shown forillustrative convenience, a lubricant topcoat is applied on theprotective overcoat 15, 15′. It should be understood that the presentinvention is applicable to the production of various types of magneticrecording media, and is not limited to any particular substratematerial, underlayer, magnetic layer, protective overcoat or lubricanttopcoat.

The magnetic recording media of the present invention may be used in aninformation storage system. The information storage system will compriseat least a head-disk assembly and control electronics which may beemployed with a computer, printer, or fax machine or other host system.Many different information storage system configurations are known inthe art, including those described in U.S. Pat. Nos. 5,097,368;5,193,046; and 5,317,463.

A simplified drawing of an exemplary information storage system is shownin FIG. 3. As shown in FIG. 3, the information storage system 100includes a sealed housing 120, a rigid magnetic recording media 140which is usually in the form of a disk, a read/write head 160, and anactuator assembly 170. The actuator assembly 170 includes an actuatorarm 180 for positioning the read/write head 160 disposed at the end ofthe actuator arm 180 over the surface of the recording medium 140.Multiple read/write heads 160 may be employed although not shown in theplan view. The read/write head 160 carries the magnetic recording mediaof the present invention. A spindle motor 110 is provided which mountsthe disk or disks 140 and spins them at a constant speed. A headerassembly 220 is provided for transferring electronic signals to and froma motor 240 which positions the actuator and the read/write head 160 asdata transferred to and from the disk 140.

Only certain embodiments of the present invention and but a few examplesof its versatility are shown and described in the present disclosure. Itis to be understood that the present invention is capable of use invarious other combinations and environments, and is capable of changesand modifications within the scope of the inventive concept as expressedherein.

1. A magnetic recording medium comprising, in this order: (a) anon-magnetic substrate, (b) a composite nickel-containing coatingcomprising a sputter deposited nickel-containing layer comprising NiPand an electrolessly deposited nickel-containing layer thereon, thecomposite nickel-containing coating having a bottom surface contactingthe non-magnetic substrate and a top surface, and (c) a magneticrecording layer on the top surface of the composite nickel-containingcoating, wherein the top surface of the composite nickel-containingcoating is a non-polished surface and has a surface roughness (Ra) ofless than about 10 Å, wherein the surface roughness (Ra) is averagedover the entire surface of the top surface of the compositenickel-containing coating.
 2. A magnetic recording medium of claim 1,wherein the top surface of the composite nickel-containing coatingdirectly contacts the magnetic layer.
 3. A magnetic recording medium ofclaim 1, wherein the non-magnetic substrate comprises glass or aglass-ceramic material.
 4. A magnetic recording medium of claim 1, theelectrolessly deposited nickel-containing layer comprises NiP.
 5. Amagnetic recording medium of claim 1, the sputter depositednickel-containing layer comprising about 15 atomic percent to about 30atomic percent Ni.
 6. A magnetic recording medium of claim 1, whereinthe sputter deposited layer has a thickness in a range of about 10 Å toabout 1000 Å.
 7. A magnetic recording medium of claim 1, wherein theelectrolessly deposited nickel-containing layer has a thickness in arange of about 0.5 microns to about 1 micron.